How much epsom salt?

[irrka]

I remember reading this somewhere on the thread but for the life of me i can't find the post now...
so, how much epsom salt do you put in the water and do you put it in every time? (i'm using a gallon jug to mix the goodies)
Thanks,
Irene

[Ray]

First of all, how much is in your fertilizer formula? Being in NYC, you need a very complete fertilizer - including calcium and magnesium - as your water is almost totally devoid of dissolved solids. Most of my customers from the area use the MSU formula for RO water, so they need to add nothing else.

All that said, for those using that formula at 100-150 ppm N, it adds about 0.1g Mg per gallon (OK, a shade less, but it's not harmful to have a bit extra). Epsom Salts (MgSO4.7H2O) is about 10% by weight magnesium, so you'd want to add about 1 gram of Epsom Salts per gallon to give the equivalent of the MSU fertilizer.

As a pound is about 2 quarts volume, a gram would be about 7/8 teaspoon, so I'd use 1 teaspoon per gallon.

[irrka]

i'm using dyna-gro at about that 100-125 ppm N (until i run out of that at which point i'll switch to MSU